1. Field of the Invention
This invention generally relates to a bicycle derailleur. More specifically, the present invention relates to a cable actuation ratio control mechanism of a bicycle derailleur, especially a bicycle rear derailleur.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle derailleur.
Typically, a derailleur has a base member and a movable member with a chain guide movably coupled to the base member via a linkage assembly (e.g., a coupling member). The base member is typically coupled to the rear triangle of the bicycle frame by a bolt that forms a B-axle for providing limited rotation with respect to the bicycle frame. The chain guide typically includes a pair of guide plates that rotatably support a guide pulley and a tension pulley between the guide plates. The chain guide is typically coupled to the movable member by a shaft that forms a P-axle for providing limited rotation of the chain guide with respect to the movable member. The linkage assembly typically includes a pair of pivotal links pivotally coupled to both the base member and the movable member. A spring typically biases the chain guide to either an innermost or outermost position relative to the rear sprockets. A bowden-type control cable with an outer sheath and an inner wire is typically coupled between the rear derailleur and a conventional shift control device. Thus, the chain guide can be moved laterally by moving the linkage assembly via the inner wire. Pulling the inner wire moves the chain guide against the biasing force of the spring, while releasing the inner wire causes the chain guide to move due to the biasing force of the spring.
In a cable actuated rear derailleur, the required amount of lateral displacement of the guide pulley is predetermined by the amount of lateral spacing between the rear sprockets. Thus, the required inner wire stroke is also automatically determined for a cable actuated rear derailleur. This means that such an inner wire stroke must be pulled in the shift operating device, and there is no free choice in designing the shift operating device in terms of the inner wire stroke for a particular cable actuated rear derailleur. This lateral (axial) displacement of guide pulley with respect to the inner wire displacement is defined as the actuation ratio of the rear derailleur.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle rear derailleur that will enhance design freedom for the shift operating device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.